The present invention is directed to an indicator for an electrical device such as a relay or the like. The electrical device will be referred to herein as a relay, but it is understood that the indicator assembly disclosed and claimed herein may be used on any similar electrical device.
There has been a need for a reliable indicator for the condition of contacts in a relay wherein the indicator does not substantially affect the operation, and particularly the speed of operation of the relay. There has also been a need to provide such an indicator for relays and equivalent electrical devices in which a clear visual indication is provided of the condition, operated or unoperated, of a relay. It is also desirable to provide a means in the indicator assembly wherein the contacts of the relay cannot be reset until the indicator element is moved back to its original position, indicating relay contacts in their unoperated state or that the relay is not energized. There has also been a need to produce a relay which is highly reliable and which does not require a separate solenoid for operation, hinges, pivot means, springs or other elements which may require periodic maintenance.
In a particular application of the present invention, there is a need in the field of high speed protective relaying utilized by the electric utility companies to provide an indicator which will indicate the condition of such high speed protective or auxiliary relays without slowing down the operation of the high speed relays. The protective or auxiliary relays are usually not operated, but are only operated when a fault, overload, open circuit, or other abnormality occurs. When a fault does occur it is desired that the relays operate very rapidly. Therefore, a protective or auxiliary relay may not be operated for a period of several years, but if a fault occurs, relay operation is required in a fraction of a second. Therefore, it is important that any indicator for the operated or unoperated condition of the relay contacts be operated from the relay contact operator in such a manner so as to avoid any slowing down of the action of the contact operator element and that elements which may result in friction in operation be eliminated. It is desirable to keep the loading of the contact operator element or the force required to be exerted by the contact operator element at a minimum.
Indicators which would utilize the structure such as spring charged latches to hold their targets in place are undesirable since such latches require considerable force on the part of the contact operator to produce unlatching when the relay is operated. Also, such spring loaded latches and other complicated mechanical structures tend to "hang up" or fail to operate as required for any number of various reasons, such as hinge pivots and latch mechanisms become "stiff" due to corrosion caused by non-use over long periods of time. However, it is highly desirable to provide an indicator which will not produce false indications caused by vibrations or other local disturbances, such as large trucks passing by or local blasting, when the relay has not been operated.